1. Technical Field of the Invention
The present invention relates to signal amplification, and particularly to a preamplifier circuit for amplifying signals generated by the read head of a disk drive device.
2. Description of the Related Art
Most computer systems include one or more associated disk drives, which may be built internal or external to the computer system. Typically, disk drives have at least one rotating magnetic medium and associated head mechanisms that are carried adjacent the magnetic material. The heads are radially positionable to selectively write information to, or read information from, precise positions on the disk medium. Such disk drives may be, for example, hard disk drives, floppy drives, or the like.
The conventional disk drive recording technology is referred to as “longitudinal magnetic recording” in which data is stored longitudinally along the surface of the magnetic recording medium in predefined concentric tracks. Data is written to the conventional data disk by applying a series of signals to a write head according to the digital information to be stored on the magnetic disk media. The write head has a coil and one or more associated pole pieces that are located in close proximity to the disk media. As signals cause the magnetic flux to change in the head, the magnetic domains of the magnetic media along the surface of the disk are aligned in predetermined directions for subsequent read operations. Typically, a small space of unaligned magnetic media disposed longitudinally along the medium surface separates each magnetic domain transition to enable successive transitions on the magnetic media to be distinguished from each other.
More recently, perpendicular recording as been discussed as a mechanism for extending magnetic recording density beyond what is believed to be attainable using longitudinal magnetic recording. In perpendicular magnetic recording, the medium is magnetized perpendicularly to the plane of the medium. Perpendicular magnetic recording system utilizes magnetic anisotropy in a direction perpendicular to the disk plane in order to increase the linear recording density. With this perpendicular magnetic recording system, recording at a remarkably higher density can be performed than a longitudinal magnetic recording system in which magnetic anisotropy in its plane direction is utilized. This is because in the perpendicular magnetic recording system, the demagnetizing field at a magnetization reversal region is very small in principle, thus enabling to narrow the magnetization transition width.
Next generation hard disk drive systems may employ the perpendicular magnetic recording technology. As such, the disk drive systems may very well require disk drive circuitry, such as preamplifiers, to possess low corner frequencies (LCFs) on the order of a few hundred kilohertz and high corner frequencies (HCFs) as high as 1 GHz or so. Such requirements result in a preamplifier having a lower LCF by a factor of approximately five, relative to LCFs of existing preamplifiers utilized in longitudinal recording. This LCF reduction is necessary because the readback signal of perpendicular recording has much lower frequency contents compared to longitudinal recording (square wave-like waveform versus lorentzian pulse waveform for longitudinal recording). Increased HCF that approximately doubles the HCF values for preamplifier circuitry in longitudinal recording systems may be required as well due to the increased data rate requirements associated with perpendicular recording. What is needed, then, is a preamplifier circuit possessing the operating performance necessary to effectively function in future disk drives utilizing the perpendicular recording technology.